Optically transparent materials (for example, glass or transparent polymers) may be used as a light guide to propagate light. A light guide typically includes at least one surface adapted to receive light from a light source and an optically smooth surface for reflecting light propagating through the light guide. Common examples of light guides include optical fibers and/or rods, and planar waveguides.
Light guides are also used as components in lighting (that is, illumination) systems. Typical light guides have an internally reflective relatively high index of refraction core and an optional lower index of refraction cladding disposed on the core. In these systems, light is injected (that is, enters at an angle less than or equal to the critical angle for internal reflection by the light guide) into at least one end of a light guide and allowed to exit the light guide at a predetermined position or positions along the length of the light guide. Methods for encouraging light to exit a light guide at a desired location are known as extraction techniques. Many extraction techniques cause light to leak from a light fiber in an uncontrolled fashion. Such techniques include subjecting the fiber to relatively sharp bends and removing and/or roughening a portion of the light guide core or cladding to provide a diffuse surface which causes light to escape. Extraction techniques using light extraction structures (for example, notches) spaced along the light fiber are also used for extracting light from a light guide in a controlled fashion.
However, the use of light guides in light systems of relatively large size has been limited by the difficulty of maintaining an acceptable, aesthetically pleasing, and reasonably uniform light intensity over relatively long lengths.